1. Field of the Invention
The present invention relates generally to a WLAN (Wireless Local Area Network) system, and more particularly to a MAC (Medium Access Control) control apparatus for use in a WLAN system.
2. Description of the Related Art
Recently, the IEEE 802.11a/g standard has been established as the latest WLAN technology standard, such that high-speed wireless equipment capable of supporting a transfer rate of 54 Mbps have recently been introduced to the market. With the increasing demands of users, networking technologies of household appliances included in a home network have also been proposed as a major issue of the WLAN technologies. Many developers have conducted extensive research into the WLAN technologies in order to increase wireless speed and data throughput, and currently attempt to raise a wireless link speed to 200 Mbps using a MIMO (Multiple Input Multiple Output) technology of the IEEE 802.11 TGn standardization group.
The MAC (Medium Access Control) layer applies a resource request scheme to a random access scheme in order to increase efficiency of radio resources, thereby raising the MAC throughput to 80%.
However, there are some problems in applying such WLAN technologies to a home network even though the wireless link speed and the MAC throughput are increased. More specifically, some problems occur in interconnecting household appliances over a wireless network due to characteristics of a variety of household appliances (e.g., digital TVs, Internet phones (i.e., VoIP (Voice over Internet Protocol) phones), game machines, audio systems, etc.) capable of providing a variety of data services, resulting in QoS (Quality of Service) support complexity, QoS setup difficulty, communication frequency band limitation, etc.
Summarizing individual data characteristics of the above-described household appliances, digital TV uses an MPEG2 data stream having a variable bit rate of 20 Mbps, and has a high variation in data rate. A VoIP phone data has a time period below 1 Mbps, and requires real-time transmission sensitive to transfer delay and jitters. Additionally, data for use in a game machine has a random period below 1 Mbps, has very weak resistance to transfer delay, and requires real-time transmission. Data for use in the audio system has a time period of about 1 Mbps, has very weak resistance to jitters, and requires a constant speed. Further, computer data is configured in the form of a large capacity file or Internet data, and is not greatly affected by transfer delay, but it has a high variation in data rate.
Generally, data characteristics for household appliances are classified into traffic data having a short delay time, random traffic data having a short delay time, and other traffic data not greatly affected by a long delay time, while simultaneously having a high variation in data rate.
The IEEE 802.11 standard established as a WLAN standard is based on a DCF transmission scheme using a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance). However, the DCF (Distributed Coordination Function) transmission scheme does not support any kind of priorities in accessing a wireless medium, such that it is difficult to guarantee a QoS. Although the DCF transmission scheme can use a PCF (Point Coordination Function) transmission scheme defined as an optional item, the PCF transmission scheme based on the DCF transmission scheme cannot separately define traffic type information, and cannot estimate a transfer time, such that it is not widely implemented up to the present time.
The EDCF (Enhanced DCF) proposed by the IEEE 802.11e standard can define eight traffic/priority types, and the high priority traffic data has an AIFS (Arbitration Inter Frame Space) of a shorter time. Additionally, an HCF (Hybrid Coordination Function) scheme has been proposed to extend the polling mechanism of PCF such that a hybrid controller polls the stations during a contention-free period and grants a specific start time and a maximum transmit duration. However, the HCF scheme must control traffic data requiring various QoSs using only one MAC entity, such that it unavoidably increases MAC complexity and has difficulty in supporting a high QoS requirement requested by the household appliances.